An electronic throttle valve system more suitable for use in straddle type vehicles. A straddle type vehicle has an electronic throttle valve system for adjusting the amount of intake air to an internal combustion engine. The electronic throttle valve system includes a throttle valve for adjusting the amount of intake air to the internal combustion engine, an electric motor for actuating the throttle valve, and a control unit for controlling the electric motor. The throttle valve is fixed to a valve shaft. The electric motor is connected to the valve shaft. The valve shaft is provided with a throttle opening sensor on the right end, and a mechanical, throttle valve actuating mechanism on the left end. A throttle cable is engaged with the mechanism, while being coupled to a throttle grip (acceleration controller) provided on a right one of a pair of handlebars.